Gas generator and method for the generation of low-temperature gas

ABSTRACT

Gas generator comprising at least one first body, comprising means for the generation of gas, and at least one second body, comprising means for the generation of a neutralisation agent, wherein means are present for contacting the said neutralisation agent with the said first body, to neutraise reaction products from the generation of gas in the said first body, and wherein means are present for operating the generation of a neutralisation agent in the second body at a temporal and/or spatial interval from the generation of gas in the first body.

The invention relates to applied chemistry, more specifically to acomposition for the generation of gases of low temperature and a processfor the obtaining of gases of low temperature.

Gas generating processes based on the decomposition or burning ofchemical propellants and other compositions are frequently being usedfor a number of purposes such as the inflation of airbags from, forinstance, cars, rafts, life boats and vests, fast installed partitions(which are used in well drifts to cut off the well in case of fire),drives and generators for different types of pneumatic systems andoperations mechanisms etc.

Some technical methods for obtaining relative cold gases, in particularnitrogen, are known. These methods are based on the decomposition or theburning of solid materials in special units. These materials aregenerally shaped in the form of monolithic or porous products and comein all types of shapes and sizes.

The hot gases generated from the decomposition of these materials are ingeneral cooled with the aid of special chemical cooling agents or byspecific designed features such as heat exchangers.

The high temperature burning gases are passed through the layer of thecooling agent or the heat exchanger and the temperature of the gasesdecreases as a result of the endothermal decomposition process of, orheat absorption by the cooling agent. Such processes are described forinstance in U.S. Pat. No. 1,362,349, GB-1371506, FR-136897 and theRussian inventors certificate 801540. The use of heat exchangers isdescribed in GB-1500137 and GB-1487944.

The degree of cooling of the generated gas depends on the nature of thecooling agent, the mass of the cooling agent, which can sometimesexceeds the mass of the gas-generating composition, and in case of theheat exchanger, the design features of exchanger.

One of the drawbacks of the prior art as cited above is the relativelycomplicated structure of these units. Another drawback is that the knowngas generators do not allow or provide for the gases to be cooled below150° C. Therefore the applicability of these gas generators is limitedto systems that can withstand such high temperatures. These aredisadvantages from cost-economic and application viewpoints.

Additionally, gases obtained by the use of the above described methodscontain large and undesired amounts of components which may not onlyhave a negative effect on the construction but also in case of airbagsfor cars, for the person (driver) who is supposed to be protected by theairbag.

Complicated design and complex products resulting in their increasingmass, size and complexity are negative features of these gas generatingmethods. This decreases reliability and efficiency of the completesystem. Especially in the life saving airbags industry there is acontinuous need for reliable, safe and economic methods for thegeneration of cold gases.

RF-patent 2108282 describes a method of generating cold gases,specifically nitrogen, but also hydrogen and oxygen, by using theendothermal decomposition of a product made of gas penetrable solidmaterial. The gas penetratable solid material comprises a gas source anda heat absorbing mixture, whereby the gaseous reaction products arecooled by passing the hot gases through the porous body of the productin the moving direction of the reaction front. The hot gases heat theporous body to a temperature necessary to support the endothermicchemical reaction taking place. The heating of the porous body isnecessary to enable the main reaction. The decomposition of the coolingagent is also an endothermic chemical reaction. The patent claims toobtain nitrogen gas from a solid propellant system with a purity betterthan 97% and a temperature below 150° C.

In the gas generator using this method (as well as in most other gasgenerators) azides, hydrides and chlorates are used as the gas source,which compounds are in general used in the form of alkali andearth-alkali compounds. On decomposition of these compound usually ahighly reactive metallic slag remains behind in the gas generator.

As an example, for a nitrogen producing gas generator composition NaN₃may be used. The decomposition reaction of NaN₃ results in Na and N₂.Likewise in other decomposition reactions of sodium compounds, alsosodium is formed. The formed gas is blown off and the slag remains. Thisslag comprises of the remains of cementing agent and, the cooling agentand the metallic sodium. Under these conditions of gas generation thehighly chemical reactive sodium is thus generated. This highly reactivematerial will accumulate in the condensed burning decomposition productsand thus provides a potential hazard for persons involved. When moistureis present this can result in vigorous and dangerous reactions takingplace in combination with the generation of the highly flammable andexplosive hydrogen. The decomposition of which might be followed byexplosions, other undesirable effects or even personal injuries, ifpersons are involved.

Methods for the neutralisation of sodium are itself known in the art andfor instance described in “Sodium production, its properties and use”,State Publishing House, Moscow, 1961 pp 142. One of the methodsdescribed for the removal of metallic sodium is destruction with water.To be able to apply this method in order to neutralise the used gasgenerator, the generator after use has to be hermetically sealed andtransported to a suitable installation to adequately neutralise thereactive remains of the generator. This is dangerous, cost-ineffective,complex and thus undesirable.

In the case of sodium-compounds as the gas source, elemental sodium (Na)is formed upon decomposition of sodiumazide. Sodium is a highly reactiveand aggressive chemical. As a result of this reactivity, sodium canreact with a wide class of substances to a number of sufficiently stablecompounds. One of these compounds is sulphur. Sodium reacts with sulphurto form sodium sulphide (Na₂S).

The neutralisation of sodium by reaction with sulphur or sulphurcompounds in gas generating compositions is known for instance from U.S.Pat. No. 3,775,199, U.S. Pat. No. 5,536,340, EP 394103 and U.S. Pat No.3,741,585. The sulphur is vaporised during the decomposition of thegas-generating composition and reacts with the formed sodium slag to theneutral sodiumsulphide.

In the gas generators of the prior art as described hereinabove, thesulphur is vaporised together with the gas generation. It is difficultto vaporise the sulphur at the same rate at which the sodium slag isformed and the rate at which it reacts with the sodium slag. As a resultvaporised sulphur will exit the gas generator and/or not all metallicsodium is neutralised. This is a drawback of the use of mixtures ofsulphur and gas-generating compositions as described in the prior art.

It is therefore a goal of the present invention to develop a productwhich will result in the effective generation of nitrogen gas of lowtemperature without the adverse effects as described above and withoutmajor concessions towards output and performance parameters of the gasgenerator.

It is another goal of the invention to provide for a process for thegeneration of nitrogen gas of low temperature and to provide for a gasgenerator which generates nitrogen gas of low temperature.

Inventors have now found a gas-generating configuration that canovercome the above-mentioned deficiencies of the prior art and resultsin the generation of low temperature gas with effective and sufficientneutralisation of the reactive slag.

The invention accordingly comprises a gas generator comprising at leastone first body, comprising means for the generation of gas, and at leastone second body, comprising means for the generation of a neutralisationagent, wherein means are present for contacting the said neutralisationagent with the said first body, to neutralise reaction products from thegeneration of gas in the said first body, and wherein means are presentfor operating the generation of a neutralisation agent in the secondbody at a temporal and/or spatial interval from the generation of gas inthe first body.

The principle of the invention encompasses the separation of gasgeneration material and neutralising material, thereby making itpossible to improve the effectivity and reliability of the gasgeneration and neutralisation. According to an embodiment of theinvention, two gas generating materials are present in one housing,spatially separated from each other. A first gas generator with theprimary task of generating gas, preferably of low temperature, and asecond gas generator with the primary task of generating neutralisingcompounds for the slag obtained from the first gas generator.

The first gas generator comprises a composition from which nitrogen,hydrogen and/or oxygen gas, preferably of low temperature can beobtained by the decomposition of a gas generating composition in theform of a gas penetrable solid material wherein the generated gaseousproducts are passed through the porous body in the direction of themoving decomposition front.

The second gas generator (the neutraliser) is another compositiongenerating a neutralising gas, preferably comprising a gas generatingcomposition together with an effective neutraliser compound, forinstance sulphur, iron oxide, metal sulphide, metal oxides (from Fe, Cu,Mg, Ti, Sn, B etc.), SiO₂ and the like. With the neutraliser compositiona neutralising gas is generated separately from the gas generated in thefirst generator. The neutralising gas is generated at a time and/orspace interval with the first gas generator. It is an important aspectof the invention, that the neutralising agent does not come into contactwith the decomposing solid porous material, during or prior to thedecomposition thereof. The invention is based on the principle, thatonly after the material has been decomposed, the neutralising materialis passed through the decomposed porous solid material, therebyneutralising the (usually hazardous) decomposition products (slag). Theneutralising gas is generated at a rate and a manner that the effectiveneutralisation of slag is accomplished and the vaporous neutralisingagent is not emitted. The neutralising agent, such as vaporous sulphur,reacts with the reaction products (slag) from the first gas generatorsuch that the these products are effectively neutralised.

In an embodiment the invention thus relates to a first gas generatorcomprising a gas penetrable solid material comprising a nitrogen source,preferably an azide, more preferably sodiumazide, cementing agent andoptionally a heat absorbing mixture, wherein the solid material has aporosity of 35-60% and a second gas generator containing a neutralisercomposition which contains sulphur and an additional nitrogen source.

The gases to be generated can be selected from the group of nitrogen,oxygen and hydrogen, or combinations thereof. Generally azides, hydridesand chlorates are used for that, preferably in the alkali metal form.

In a further embodiment of the invention the gas to be produced isnitrogen, the nitrogen sources in both the first and the second gasgenerator are selected from the group of alkalimetal azides or anearth-alkalimetal azides, preferably potassium azide or sodium azide,more preferably sodium azide.

The first and second gas generator do not have to be physicallyseparated from each other. In embodiments of the invention they can beplaced in any position relative to each other, as long as the vaporisedneutraliser of the second generator can come into contact with the slagfrom the first generator.

In the invention, the neutralisation takes place behind the reactionfront of the decomposition reaction of the first gas generator. Thespatial interval between the said reaction front of the first gasgenerator and production of the neutralising agent in the second gasgenerator is such that the reaction products of high temperature fromthe first gas generator stay behind, while the nitrogen gas is blownoff. The neutralisation front lags behind the decomposition front andneutralises the said reaction products remaining behind.

In another embodiment of the invention the rate at which the gasgenerating composition decomposes is different from the decompositionrate of the neutraliser charge. Thus, the decomposition of the gasgenerating composition and the neutraliser are started simultaneously.Metallic slag is formed, followed by the generation of vaporousneutraliser in the second generator, which neutralises the slag.

In another embodiment of the invention the moment at which theneutraliser is activated lies later than the moment of activation of thegas generator.

The activation, or ignition, of the two bodies can be done by anysuitable means known in the art.

A typical embodiment of the invention is as follows.

A body consists essentially of two parts: the gas generator and theneutraliser. The gas generator will contain a porous solid material,containing a gas generating component such as sodiumazide, together withcementing agents (such as phenolic resins) and optionally cooling agentsor other heat absorbing mixtures. The other part of the body is theneutraliser mass. The neutraliser contains the neutraliser (sulphur,iron, metal sulphides, metal oxide) and a gas generating component. Thegas-generating component may be identical to the gas generatingcomponent in the first part, for instance sodiumazide. When the gasgenerator is activated, gas is generated and blown off, leaving behindhighly reactive metallic sodium slag. The neutraliser is activated andthe neutralising reagent is vaporised; in the case of solid neutralisingagents it may be brought in aerosol form. The neutraliser will reactwith the slag, resulting in non-hazardous or less hazardous materials,in the case of neutralising sodium with sulphur, resulting in theneutral sodiumsulphide.

The amount of neutraliser is such that it is sufficient to effectivelyneutralise the slag formed in both the neutraliser and the gas generatorand that only minimal or almost no vaporous neutraliser is blown off.

In the present invention, in order to facilitate the interaction betweenthe sodium and the neutraliser compound (e.g. sulphur) it is preferredthat the neutralisation product is in a form in which the reaction withthe sodium slag is enhanced. To this extent the neutraliser can be mixedwith the gas-generating compound in the form of powder, granules, etc.

In a gas generator according a preferred embodiment of the invention,said gas generator being based upon the use of sodium azide and sulpur,the combined amounts of the nitrogen sources in the first and secondbody comprises 50-80 wt. % drawn on the total weight of the gasgenerator and the amount of neutralisation agent in the second body47-90 wt. % of neutralisation agent, drawn on the weight of the secondbody. The respective weight of the gas generator is measured in theabsence of housing, external cooling aids, etc.

The second body (gas generator) comprises between 17 and 35 wt. % of thegas generator according to the invention, drawn on the total weight ofthe gas generator. The second body (gas generator) contains 10 to 53 wt.% of the nitrogen source and 47 to 90 wt. % of neutralising agent. In apreferred embodiment the second body (gas generator) contains 15 to 25wt. %, more preferable 17 to 23 wt. % of nitrogen source and 75 to 85wt. %, more preferable 77 to 83 wt. % of sulphur.

In a preferred embodiment the sulphur is in a particulate form,preferably in the form of small particles, more preferably in the formof sulphur powder.

The relative amounts of sodium azide and sulphur are contained betweenthe lower limit of sulphur which that is the amount of sulphur necessaryfor the neutralisation of the elemental sodium formed. The upper limitof sulphur is determined by the amount at which almost no vaporisedsulphur will be blown off or the amount that is considered acceptablewith respect to output gas purity.

The rate at which the gas was generated was determined in order toprovide for an optimal formulation together with the optional heatabsorbing product and the neutraliser product. The ratio of thedifferent components (nitrogen source, heat absorbing material andsulphur) was chosen such that the required maximum discharge ofvaporised sulphur and the stable burning of the material was obtained.It was found that a stable ignition and burning of the material was notpossible if the concentration of the sulphur in the material was morethan 90 wt. % of the combined weight of additional nitrogen source andsulphur (neutraliser mass). If the concentration of sulphur was below 47wt. % of said combined weight, the discharge of vaporised sulphurdecreased below the desired level and the total (neutralisermass)/(nitrogen source) ratio had to be increased in order to obtain thebonding of the elemental sodium in sufficiently high levels. Thepreferred mass ratio of the nitrogen source and the neutraliser isdetermined by the total neutralisation of sodium to sodium sulphide inthe slag.

In a preferred embodiment of the invention the nitrogen source and theneutraliser, preferably sulphur, are homogeneously mixed as part of thesecond body.

In another preferred embodiment of the invention, the neutraliserproduct comprises sulphur and additional nitrogen source in an amount of10-53 wt. % of the additional nitrogen source and 47-90 wt. % ofsulphur, based on the combined weight thereof.

In this embodiment of the invention, the combined amount of the nitrogensource and sulphur, based on the total weight of the product is from 17to 35 wt. %.

In case the combined amount of the additional nitrogen source and thesulphur is less than 17 wt. %, the total neutralisation of sodium isinsufficient because of lack of sulphur. In case the amount is above 35wt. %, the vaporised sulphur will be blown off with the generated gasand thus the purity of the generated nitrogen gas decreases.

It is to be noted that in some cases the generated gas may contain someentrained contaminants. If these are undesirable in the intended use ofthe generator, it may be advantageous to include additional downstreamfilter means. This may be any kind of filter, such as sand, chemicalfilters, metal wire filters and the like. In some instances it may alsobe advantageous to include some additional neutralising agent in thefilter, thereby providing an additional safeguard against contaminantsbeing blown out with the gas.

In the case of generating a cold gas by passing the generated gasthrough the porous solid material, as described above, the situation mayoccur that when the material is almost completely decomposed, thecooling capacity of the remainder of the porous material is too small tomaintain the temperature of the gas at a constant level. If in aspecific application this is not acceptable, it can be advantageous toinclude downstream cooling means in the gas generator. It is possible tocombine these cooling means with filter means discussed above,especially as both the cooling means and the filter means can easily beconstructed from the same materials (sand, steel wire, steel wool, metalmesh and the like).

The invention also relates to a process for the generation of gases,preferably nitrogen, comprising the steps of:

-   -   decomposition of a gas-penetrable porous solid material in a        first body, whereby gas and other reaction products are        generated at a decomposition front;    -   generating a neutralisation agent in a second body;    -   neutralising the said other reaction products in the first body        by reaction with the neutralisation agent;    -   maintaining a temporal and/or spatial interval between the        decomposition front of the first body and a neutralisation front        obtained by passing the neutralisation agent from the second        body into the first body.

Upon ignition of the nitrogen source containing gas generating materialand the neutralisation material, the materials start decomposing. Thegaseous decomposition products of the nitrogen source pass through theramified porous body in the moving direction of the reaction front andare cooled by transferring heat to the porous body. At the burning ofthe neutraliser, vaporised sulphur is generated and passed through theslag of the nitrogen source. In an embodiment of the invention a spatialand temporal interval between the reaction front of the nitrogen sourceand the reaction front of the neutraliser is provided. The reactionbetween the vaporised sulphur and the metallic sodium is exothermic.However, as there is a spatial and/or temporal interval between the gasgeneration and the neutralisation, this will not influence thetemperature of the generated gas. This interval can be accomplished by alower reaction rate of the neutraliser when compared to the reactionrate of the nitrogen source or by a suitable time delay. By thisinterval the vaporised sulphur is mainly generated after the sodium isformed, thus allowing for more optimal reaction conditions for both thegeneration of gas and the neutralisation of sodium.

The interval can also be controlled by design related features such asthe adjustment of the flow rates by a different form of the burningsurface or by the non-simultaneous ignition of the nitrogen source andthe neutraliser. The invention accordingly comprises a generator for lowtemperature gas.

In a preferred embodiment the generated gases are cooled by passing thegases through a porous body in the moving direction of the reactionfront.

In an preferred embodiment heat is absorbed which is formed in theexothermic reaction by a heat absorbing material included in the porousbody.

In a preferred embodiment of the invention the amount of heat generatedin relation to the amount absorbed heat is such that the generated gasis cooled to a temperature below 150° C., preferably below 100° C.

The invention is now elucidated on the basis of the attached figure. Inthe figure a gas generator is shown, having a housing 1, provided withan opening 2, for generated gas. In the housing 1, two gas generatingbodies 3,4 are present. A first solid porous body 3, providing the majoramount of gas, and a body 4, providing a neutralising gas. Further abody 5 of cooling and/or filter material is present, for example a sandfilter, optionally containing a dispersed additional neutralising agent.

Once the body 3 has been ignited by igniting means (not shown), thedecomposition starts, resulting in the production of a gas, which flowsmainly in the direction of the arrows B, i.e. through the body 3,thereby heating the porous material, at the same time as being cooled toa relatively low temperature. Finally the cooled gases leave the housing1, through opening 2 in the direction of arrows C.

The decomposition of the porous solid material proceeds with time andthe decomposition front moves in the direction of arrow A.

From body 4, a neutralising gas is produced, after ignition of the body(by ignition means, not shown). The gas flows in the direction of arrowsD and creates a neutralisation front (not shown) in body 3, which frontstays behind the decomposition front, but moves in the same direction(arrow A).

1. Gas generator comprising at least one first body, comprising meansfor the generation of gas, and at least one second body, comprisingmeans for the generation of a neutralisation agent, wherein means arepresent for contacting the said neutralisation agent with the said firstbody, to neutralise reaction products (slag) from the generation of gasin the said first body, and wherein means are present for operating thegeneration of a neutralisation agent in the second body at a temporaland/or spatial interval from the generation of gas in the first body. 2.Gas generator according to claim 1, wherein the said means forgenerating a gas comprise components that generate nitrogen, oxygen,hydrogen or combinations thereof.
 3. Gas generator according to claim 2,wherein the means in the first body comprise a gas-penetrable solidmaterial comprising a gas source, cementing agent and optionally a heatabsorbing mixture, wherein the solid material has a porosity of 35-60wt. %.
 4. Gas generator according to claim 1, wherein said first bodycomprises means for generating nitrogen, preferably an azide, morepreferably sodium azide.
 5. Gas generator according to claim 1, whereinthe reaction products comprise slag containing sodium.
 6. Gas generatoraccording to any of the claim 1, wherein the second body contains a gassource and a neutralising agent.
 7. Gas generator according to any ofthe claim 1, wherein the neutralisation agent is sulphur.
 8. Gasgenerator according to any of the claim 1, wherein the combined amountsof the gas, preferably nitrogen sources in the first and second bodycomprises 50-80 wt. % drawn on the total weight of the gas generator andthe amount of neutralisation agent in the second body 47-90 wt. % ofneutralisation agent, drawn on the weight of the second body.
 9. Gasgenerator according to any of the claim 1, wherein the second body isbetween 17 and 35 wt. %, drawn on the total weight of the gas generator.10. Gas generator according to any of the claim 1, wherein the secondbody contains 10 to 53 wt. % of the nitrogen source and 47 to 90 wt. %of the neutralisation agent.
 11. Gas generator according to any of theclaim 1, wherein the generated gases are cooled by a heat absorbingmaterial.
 12. Gas generator according to any of the claim 1, whereby theheat absorbing material is included in the first body.
 13. Gas generatoraccording to claim 1, wherein downstream from the first body means arepresent for cooling and/or filtering the gases.
 14. Gas generatoraccording to claim 1, wherein said means also comprise neutralisingagents for contaminants entrained in the gas.
 15. Gas generatoraccording to claim 1, wherein the said first and second bodies arecontained within one container, said container having at least oneoutlet for generated gas.
 16. Process for the generation of gases,preferably nitrogen, comprising the steps of: decomposition of agas-penetrable porous solid material in a first body, whereby gas andother reaction products are generated at a decomposition front;generating a neutralisation agent in a second body; neutralising thesaid other reaction products in the first body by reaction with theneutralisation agent; maintaining a temporal and/or spatial intervalbetween the decomposition front of the first body and a neutralisationfront obtained by passing the neutralisation agent from the second bodyinto the first body.
 17. Process according to claim 16, wherein thegenerated gases are cooled by passing the gases through the porous solidmaterial in the same direction as the reaction front is moving. 18.Process according to claim 16, wherein heat is absorbed in the porousbody, which heat is formed in the decomposition of the gas-penetrableporous solid material.
 19. Process according to claim 16, wherein theamounts of heat formed and absorbed are such that the generated gas iscooled to a temperature below 150° C., preferably 100° C.
 20. Processaccording to claim 17, wherein the heat absorbed in the porous solidmaterial maintains the temperature necessary for decomposition of thegas-penetrable porous solid material.
 21. Process according to claim 16,wherein the generated gases are passed through a filter and/or coolingmeans, downstream from the generation of the gases, said filter and/orcooling means optionally containing further neutralisation means.